Figure 6. Resistance to GL261 tumor growth in PD-1H–KO mice is mediated by CD4⁺ T cell immunity.

3 × 10⁵ GL261-luc tumor cells were injected into the left hemisphere of the brains of PD-1H–KO or WT mice. Mice were treated with a total dose of 4 Gy radiotherapy of the whole brain on day 5 after tumor inoculation. (A) Ten days after radiotherapy, splenocytes and brain lymphocytes were isolated and restimulated with irradiated GL261 cells for 5 days. Percentages of IFN-γ–producing CD4⁺ T cells of total CD4⁺ T cells (left panels) or IFN-γ–producing CD8⁺ T cells of total CD8⁺ T cells (middle panels) were detected by intracellular staining. IFN-γ levels in culture supernatant were detected by CBA (right panels). One point indicates the result from 1 mouse (n = 6). Naive mice (n = 2) without tumor inoculation were used as negative control. (B) CD4⁺ T cells or CD8⁺ T cells were depleted by i.p. injection of anti-CD4 (GK1.5) or anti-CD8a (53-6.72) antibody at 500 μg every 5 to 7 days from 5 days before tumor inoculation. Survival of mice was monitored daily up to 50 days (n = 5). *P < 0.05; **P < 0.01.